This invention relates to wellbore fluids suitable for use in oil and gas exploration and production industries and embraces the fluids used for drilling, under-reaming, completion, cementing, fracturing, stimulation, workover and packing of wellbores and also includes spacer fluids whose function is to separate two fluids during pumping operations and spotting fluids whose function is to treat certain intervals of the wellbore.
In the process of rotary drilling a well, a drilling fluid or mud is being circulated down the rotating drill pipe, through the bit, and up the annular space between the pipe and the formation or steel casing, to the surface. The drilling fluid performs different functions such as removal of drilled cuttings from the bottom of the hole to the surface, suspension of cuttings and weighting material when circulation is interrupted, control of subsurface pressures, maintaining the integrity of the wellbore until the well section is cased and cemented, isolate the fluids from the formation by providing sufficient filtration control to prevent excessive loss of fluids to the formation, cool and lubricate the drill string and bit, maximise penetration rate etc.
The required functions can be achieved by a wide range of fluids composed of various combination of solids, liquids and gases and classified according to the constitution of the continuous phase mainly in two groupings: aqueous (water-based) drilling fluids, and non-aqueous (mineral oil or synthetic-base) drilling fluids, commonly xe2x80x98oil-base fluidsxe2x80x99
Other types of fluid used in well operations include completion fluids, a term which commonly refers to fluids pumped after drilling finishes but prior to starting production, and workover fluids, used in remedial operations usually on a well that is already producing.